Since 1982 more than 150 hospitals, primarily North American Level I and Level II trauma centers, have submitted data on more than 170,000 seriously injured patients to the American College of Surgeons Committee on Trauma Major Trauma Outcome Study (MTOS). MTOS has accumulated the largest and most consistently processed database of injury severity and outcome in existence. Since April 1987, patient data have been collected under controlled conditions at four Level I trauma centers ("controlled sites") and through 1989 data from approximately 18,000 of their patients will have been collected. The MTOS database provides a unique opportunity for outcome related research to extend and improve institutional care evaluations and quality assurance activities and to identify an improved basis for trauma care reimbursement. Controlled site data will be used to evaluate TRISS norms and compare TRISS and ASCOT outcome predictions; to determine the effect of preinjury illness on outcome; to develop relationships for predicting the occurrence of serious complications, for patient disability at discharge from acute care and for lengths of stay in hospital and in ICU. Relationships between ACS and JCAHO audit filters and patient outcomes will be investigated. All controlled site data will be coded in AIS-90 and associated survival/death outcome norms developed for use in the early 1990's.